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Energy
is a prominent and highly visible form of energy transfer.}} Energy (from Latin Energia and Greek Ενεργεια) is a measure of the ability to do .This definition is one of the most common; e.g. Glossary at the NASA homepage It is a fundamental pertaining to the ability for . In , it is a that every possesses. This quantity is not absolute but relative to a state of the system known as its state or reference level. The energy of a physical system is defined as the amount of that the system can produce if it changes its state to its reference state; for example if a of cools down to 0 or if a car hits a tree and decelerates from 120 to 0 . Types of energy Energy can be in several forms: mechanical —due to possible physical interactions with other objects (for example, ); —contained in macroscopic ; —potential stored in between ; —potential due to possible interactions; —contained in the kinetic energy of individual ; —potential stored between constituents of . Light can be viewed as energy in the form of or s, depending on context. The theory of provides a framework to envision itself as an expression of energy. KARIEBI WAS HERE! WIKIA IS FAKE! Conservation of energy One form of energy can be readily transformed into another; for instance, a battery converts into , which can be converted into . Similarly, is converted into of moving and in a , which in turn transforms into by . The law of states that in a the total amount of energy, corresponding to the sum of a system's constituent energy components, remains constant. This law follows from of , which states the independence of any physical process on the moment it started. Some works, thus some forms of energy, are not easily measured by the unaided observer. Alternative uses of the term The term "energy" is also used in a or non-scientific way that cannot be quantified, to make certain propositions appear more plausible, by imitating the scientific terminology. Usually this has something to do with and/or type references such as and . Psychical researchers will often speak of so-called " energy" when attempting to explain phenomena such as activity; this is likewise non science http://www.whyprophets.com/prophets/non_science.htm. Forms of Energy * : the energy of moving objects ** : the energy associated with heat ** : the energy of compression waves ** : the energy of moving charged particles * : the energy that an object has due to position; also known as stored energy ** : the stored energy of chemical substances ** : the stored energy of the atomic nucleus * : the energy of , including light Units SI The unit for both energy and work is the (J), named in honour of and his experiments on the . In slightly more fundamental terms, 1 joule is equal to 1 - and, in terms of s: 1\ \mathrm{J} = 1\ \mathrm{kg} \left( \frac{\mathrm{m}}{\mathrm{s}} \right ) ^ 2 = 1\ \frac{\mathrm{kg} \cdot \mathrm{m}^2}{\mathrm{s}^2} An energy unit that is used in is the (eV). One eV is equivalent to . In the unit cm-1 = 0.0001239 eV is used to represent energy since energy is inversely proportional to wavelength from the equation E = h \nu = h c/\lambda . (Note that , which is typically expressed in newton-meters, has the same dimension and this is not a simple coincidence: a torque of 1 newton-meter applied on 1 radian requires exactly 1 newton-meter=joule of energy.) Other units of energy In cgs units, one erg is 1 g cm2 s−2, equal to 1.0×10−7 J. The / for both energy and work include the (1.3558 J), the (Btu) which has various values in the region of 1055 J, and the -hour (2.6845 MJ). The energy unit used for everyday , particularly for utility bills, is the (kW h), and one kW h is equivalent to (3600 kJ or 3.6 MJ; the metric units usually are self-consistent, and this particular one may seem arbitrary; it's not, the metric measurement for time is the second, and there are 3,600 seconds in an hour -- in other words, 1 kW second = 1 kJ, but the kW h is a more convenient unit for everyday use). The is mainly used in nutrition and equals the amount of necessary to raise the of one of by 1 degree, at a of 1 . This amount of heat depends somewhat on the initial temperature of the water, which results in various different units sharing the name of "calorie" but having slightly different energy values. It is equal to . The calories used for in nutrition are the large calories based on the kilogram rather than the gram, often identified as food calories. These are sometimes called kilocalories with that calorie being the small calorie based on the gram, and as a result the prefixes are generally avoided for the large calories (i.e., 1 kcal is 4.184 kJ, never 4.184 MJ, even if "calories" are also used for the other, larger unit in the same document or the same nutrition label). Food calories are sometimes noted as C''alories (1000 calories) or simply abbreviated Cal with the capital C, but that convention is more often found in chemistry or physics textbooks—which do not use these large calories—than it is in real-world applications by those who do use these calories. (This convention is also, of course, useless when the word calorie appears in a location where it would ordinarily be capitalized, as at the beginning of a sentence or in the first column of a nutrition label as a substitute for the quantity being measured, which is energy, when all the other quantities such as "Iron" and "Sugars" are also capitalized.) Transfer of energy Work main|Mechanical work ''Work is a defined as a integral of force F over distance s: W = \int \mathbf{F} \cdot \mathrm{d}\mathbf{s} The equation above says that the work ( W ) is equal to the integral of the of the ( \mathbf{F} ) on a body and the of the body's ( \mathbf{s} ). Heat main|Heat Heat is the common name for of an object that is due to the motion of the and that constitute the object. This motion can be (motion of molecules or atoms as a whole); (relative motion of atoms within molecules) or (motion of the atoms of a molecule about a common centre). It is the form of energy which is usually linked with a change in or in a change in of . In , heat is the amount of energy which is absorbed or released when atoms are rearranged between various molecules by a . The relationship between heat and energy is similar to that between work and energy. Heat flows from areas of high to areas of low temperature. All objects (matter) have a certain amount of internal energy that is related to the random motion of their atoms or molecules. This internal energy is directly proportional to the temperature of the object. When two bodies of different come in to thermal contact, they will exchange internal energy until the is equalised. The amount of energy transferred is the amount of heat exchanged. It is a common misconception to confuse heat with internal energy, but there is a difference: the change of the internal energy is the heat that flows from the surroundings into the system plus the work performed by the surroundings on the system. Heat Energy is transferred in three different ways: , and/or . Conservation of energy The first law of says that the total inflow of energy into a system must equal the total outflow of energy from the system, plus the change in the energy contained within the system. This law is used in all branches of physics, but frequently violated by quantum mechanics (see ). relates the to the of physical laws. An example of the conversion and is a . At its highest points the is zero and the is at its maximum. At its lowest point the is at its maximum and is equal to the decrease of . If one unrealistically assumes that there is no , the energy will be conserved and the will continue swinging forever. (In practice, available energy is never perfectly conserved when a system changes state; otherwise, the creation of machines would be possible.) Another example is a in which is converted to and in a very short time. Relations between different forms of energy All forms of energy: , , , , etc. can be in fact reduced to or . For example is essentially of and ; can be visualized to be the of within ; can be visualized to be the and of ; similarly is the of in . Kinetic energy is the portion of energy related to motion. : E_k = \int \mathbf{v} \cdot \mathrm{d}\mathbf{p} The equation above says that the kinetic energy ( E_k ) is equal to the integral of the of the ( \mathbf{v} ) of a body and the of the body's ( \mathbf{p} ). For non- velocities, that is velocities much smaller than the , we can use the : E_k = \begin{matrix} \frac{1}{2} \end{matrix} mv^2 where E''k is ''m is of the body v'' is of the body At near-light velocities, we use the correct formula: : E_k = m c^2 (\gamma - 1) = \gamma m c^2 - m c^2 \;\! : \gamma = \frac{1}{\sqrt{1 - (v/c)^2}} where ''v is the of the body m'' is its ''c is the in a , which is approximately 300,000 kilometers per second \gamma m c^2 \, is the total energy of the body m c^2 \, is again the energy. See also, . In the form of a , the formula can be written as: : E_k = \frac{1}{2} mv^2 - \frac{3}{8} \frac{mv^4} {c^2} + \cdots Hence, the second and higher terms in the series correspond with the "inaccuracy" of the Newtonian approximation for kinetic energy in relation to the formula. However, the phrase "conservation of energy" is often confusing to a non scientist. This is so, because of the common usage of the terms "save energy" or conserve energy" used in campaigns for conservation of energy resources like electricity or fossil fuels. Potential energy In contrast to , which is the energy of a due to its , or the internal motion of its particles, the of a system is the energy associated with the spatial configuration of its components and their interaction with each other. Any number of particles which exert forces on each other automatically constitute a system with potential energy. Such forces, for example, may arise from interaction (see ), or . In an isolated system consisting of two stationary objects that exert a force f(x) on each other and lie on the x-axis, their is most generally defined as : E_p = -\int f(x) \, dx where the force between the objects varies only with x and is along the line connecting the two objects. To further illustrate the relationship between and , consider the same system of two objects situated along the x-axis. If the due to one of the objects at any point x is U(x) , then the force on that object at x is : f(x) = -\frac{dU(x)}{dx} This mathematical relationship demonstrates the direct connection between and : the between two objects is in the direction of decreasing , and the magnitude of the is proportional to the extent to which decreases. A large is associated with a large decrease in , while a small is associated with a small decrease in . Notice how, in this case, the on an object depends entirely on its . These two relationships – the definition of based on , and the dependence of on – show how the concepts of and are intimately linked: if two objects do not exert forces on each other, there is no between them. If two objects do exert forces on each other, then naturally arises in the system as part of the system's total energy. Since arises from forces, any change in the system's spatial configuration will either increase or decrease the system's as the objects are repositioned. When a system moves to a lower state, energy is either released in some form or converted into another form of energy, such as . The can be "stored" as , , , or , but arises in all cases from the spatial positioning and interaction of objects within a system. Unlike , which exists in any moving body, exists in any body which is interacting with another object. For example a released above the initially has resulting from the of the Earth, which is transferred to as the acts on the object and its is decreased as it falls. Equation: : E_p = mgh \; where m'' is the mass, ''h is the and g'' is the value of due to at the Earth's surface (see ). Internal energy ''Internal energy is the associated with the motion of s, and the associated with the , and energy of s within molecules. , like energy, is a quantifiable of a system. History In the past, energy was discussed in terms of easily observable effects it has on the of objects or changes in state of various systems. Basically, if something changed, some sort of energy was involved in that change. As it was realized that energy could be stored in objects, the concept of energy came to embrace the idea of the potential for change as well as change itself. Such effects (both potential and realized) come in many different forms; examples are the stored in a battery, the stored in a piece of food, the of a water heater, or the of a moving train. To simply say energy is "change or the potential for change", however, misses many important examples of energy as it exists in the physical world. The concept of energy and work are relatively new additions to the physicist’s toolbox. Neither nor made any contributions to the theoretical model of energy, and it was not until the middle of the 19th century that these concepts were introduced. The development of required engineers to develop concepts and formulas that would allow them to describe the and efficiencies of their systems. Engineers such as and , mathematicians such as and , and amateurs such as all contributed to the notions that the ability to perform certain tasks, called work, was somehow related to the amount of energy in the system. The nature of energy was elusive, however, and it was argued for some years whether energy was a substance (the ) or merely a physical quantity, such as . William Thomson ( ) amalgamated all of these laws into his laws of , which aided in the rapid development of energetic descriptions of chemical processes by , , . In addition, this allowed to describe entropy in mathematical terms, and to discuss, along with , the laws of . For further information, see the , statistical mechanics, and random processes. Energy and Economy Main articles: and The way in which humans use energy is one of the defining characteristics of an economy. The progression from animal power to , then the and , are key elements in the development of modern civilization. , for example of , may be key to avoiding the . See also * * Energy in natural sciences * * * * * * * * * Energy resources * * * * * * * * * * * * * , * Further reading * . Six Easy Pieces: Essentials of Physics Explained by Its Most Brilliant Teacher. Helix Book. See the chapter "conservation of energy" for Feynman's explanation of what energy is and how to think about it. * (1952). Relativity: The Special and the General Theory (Fifteenth Edition). ISBN 0-517-88441-0 * (1956). Elements of Mathematical Biology, forerly published as 'Elements of Physical Biology', Dover, New York. Notes External links *Energy Business Review *What does energy really mean? From Physics World *Glossary of Energy Terms * International Energy Agency IEA - * 'Actual' (First-Law) Energy in Relation to Free Energy and Entropy Category:Measurable quantities